STEVENS, J., dissenting Berger v. United States, 295 U. S. 78, 88 . . . (1935).” The standard for judging the consequences of prosecutorial misconduct during grand jury proceedings is essentially the same as the standard applicable to trials. In United States v. Mechanik, 475 U. S. 66 (1986), we held that there was "no reason not to apply [the harmless error rule] to 'errors, defects, irregularities, or variances' occurring before a grand jury just as we have applied it to such error occurring in the criminal trial itself," id., at 71-72. We repeated that holding in Bank of Nova Scotia v. United States, 487 U. S. 250 (1988), when we rejected a defendant's argument that an indictment should be dismissed because of prosecutorial misconduct and irregularities in proceedings before the grand jury. Referring to the prosecutor's misconduct before the grand jury, we "concluded that our customary harmlesserror inquiry is applicable where, as in the cases before us, a court is asked to dismiss an indictment prior to the conclusion of the trial." Id., at 256. Moreover, in reviewing the instances of misconduct in that case, we applied precisely the Although the majority in Ciambrone did not agree with Judge Friendly's appraisal of the prejudicial impact of the misconduct in that case, it also recognized the prosecutor's duty to avoid fundamentally unfair tactics during the grand jury proceedings. Judge Mansfield explained: "On the other hand, the prosecutor's right to exercise some discretion and selectivity in the presentation of evidence to a grand jury does not entitle him to mislead it or to engage in fundamentally unfair tactics before it. The prosecutor, for instance, may not obtain an indictment on the basis of evidence known to him to be perjurious, United States v. Basurto, 497 F. 2d 781, 785-86 (9th Cir. 1974), or by leading it to believe that it has received eyewitness rather than hearsay testimony, United States v. Estepa, 471 F. 2d 1132, 1136-37 (2d Cir. 1972). We would add that where a prosecutor is aware of any substantial evidence negating guilt he should, in the interest of justice, make it known to the grand jury, at least where it might reasonably be expected to lead the jury not to indict. See ABA Project on Standards for Criminal Justice-the Prosecution Function, §3.6, pp. 90-91." 601 F. 2d, at 623. STEVENS, J., dissenting same standard to the prosecutor's violations of Rule 6 of the Federal Rules of Criminal Procedure and to his violations of the general duty of fairness that applies to all judicial proceedings. This point is illustrated by the Court's comments on the prosecutor's abuse of a witness: "The District Court found that a prosecutor was abusive to an expert defense witness during a recess and in the hearing of some grand jurors. Although the Government concedes that the treatment of the expert tax witness was improper, the witness himself testified that his testimony was unaffected by this misconduct. The prosecutors instructed the grand jury to disregard anything they may have heard in conversations between a prosecutor and a witness, and explained to the grand jury that such conversations should have no influence on its deliberations. App. 191. In light of these ameliorative measures, there is nothing to indicate that the prosecutor's conduct toward this witness substantially affected the grand jury's evaluation of the testimony or its decision to indict." 487 U. S., at 261. Unquestionably, the plain implication of that discussion is that if the misconduct, even though not expressly forbidden by any written rule, had played a critical role in persuading the jury to return the indictment, dismissal would have been required. In an opinion that I find difficult to comprehend, the Court today repudiates the assumptions underlying these cases and seems to suggest that the court has no authority to supervise the conduct of the prosecutor in grand jury proceedings so long as he follows the dictates of the Constitution, applicable statutes, and Rule 6 of the Federal Rules of Criminal Procedure. The Court purports to support this conclusion by invoking the doctrine of separation of powers and citing a string of cases in which we have declined to impose categori STEVENS, J., dissenting cal restraints on the grand jury. Needless to say, the Court's reasoning is unpersuasive. Although the grand jury has not been "textually assigned" to "any of the branches described in the first three Articles" of the Constitution, ante, at 47, it is not an autonomous body completely beyond the reach of the other branches. Throughout its life, from the moment it is convened until it is discharged, the grand jury is subject to the control of the court. As Judge Learned Hand recognized over 60 years ago, “a grand jury is neither an officer nor an agent of the United States, but a part of the court." Falter v. United States, 23 F.2d 420, 425 (CA2), cert. denied, 277 U. S. 590 (1928). This Court has similarly characterized the grand jury: "A grand jury is clothed with great independence in many areas, but it remains an appendage of the court, powerless to perform its investigative function without the court's aid, because powerless itself to compel the testimony of witnesses. It is the court's process which summons the witness to attend and give testimony, and it is the court which must compel a witness to testify if, after appearing, he refuses to do so." Brown v. United States, 359 U. S. 41, 49 (1959). See also Blair v. United States, 250 U. S. 273, 280 (1919) ("At the foundation of our Federal Government the inquisitorial function of the grand jury and the compulsion of witnesses were recognized as incidents of the judicial power of the United States"); United States v. Calandra, 414 U. S. 338, 346, and n. 4 (1974). This Court has, of course, long recognized that the grand jury has wide latitude to investigate violations of federal law as it deems appropriate and need not obtain permission from either the court or the prosecutor. See, e. g., id., at 343; Costello v. United States, 350 U. S. 359, 362 (1956); Hale v. Henkel, 201 U. S. 43, 65 (1906). Correspondingly, we have acknowledged that "its operation generally is unrestrained STEVENS, J., dissenting by the technical procedural and evidentiary rules governing the conduct of criminal trials." Calandra, 414 U. S., at 343. But this is because Congress and the Court have generally thought it best not to impose procedural restraints on the grand jury; it is not because they lack all power to do so.10 To the contrary, the Court has recognized that it has the authority to create and enforce limited rules applicable in grand jury proceedings. Thus, for example, the Court has said that the grand jury "may not itself violate a valid privilege, whether established by the Constitution, statutes, or the common law." Id., at 346. And the Court may prevent a grand jury from violating such a privilege by quashing or modifying a subpoena, id., at 346, n. 4, or issuing a protective order forbidding questions in violation of the privilege, Gravel v. United States, 408 U. S. 606, 628-629 (1972). Moreover, there are, as the Court notes, ante, at 49, a series of cases in which we declined to impose categorical restraints on the grand jury. In none of those cases, however, did we question our power to reach a contrary result.11 Although the Court recognizes that it may invoke its supervisory authority to fashion and enforce privilege rules applicable in grand jury proceedings, ibid., and suggests that 10 Indeed, even the Court acknowledges that Congress has the power to regulate the grand jury, for it concedes that Congress "is free to prescribe" a rule requiring the prosecutor to disclose substantial exculpatory evidence to the grand jury. Ante, at 55. 11 In Costello v. United States, 350 U. S. 359, 363 (1956), for example, the Court held that an indictment based solely on hearsay evidence is not invalid under the Grand Jury Clause of the Fifth Amendment. The Court then rejected the petitioner's argument that it should invoke "its power to supervise the administration of justice in federal courts" to create a rule permitting defendants to challenge indictments based on unreliable hearsay evidence. The Court declined to exercise its power in this way because "[n]o persuasive reasons are advanced for establishing such a rule. It would run counter to the whole history of the grand jury institution, in which laymen conduct their inquiries unfettered by technical rules. Neither justice nor the concept of a fair trial requires such a change." Id., at 364. STEVENS, J., dissenting it may also invoke its supervisory authority to fashion other limited rules of grand jury procedure, ante, at 48-49, it concludes that it has no authority to prescribe "standards of prosecutorial conduct before the grand jury," ante, at 46-47, because that would alter the grand jury's historic role as an independent, inquisitorial institution. I disagree. We do not protect the integrity and independence of the grand jury by closing our eyes to the countless forms of prosecutorial misconduct that may occur inside the secrecy of the grand jury room. After all, the grand jury is not merely an investigatory body; it also serves as a "protector of citizens against arbitrary and oppressive governmental action." United States v. Calandra, 414 U. S., at 343. Explaining why the grand jury must be both "independent" and "informed," the Court wrote in Wood v. Georgia, 370 U.S. 375 (1962): "Historically, this body has been regarded as a primary security to the innocent against hasty, malicious and oppressive persecution; it serves the invaluable function in our society of standing between the accuser and the accused, whether the latter be an individual, minority group, or other, to determine whether a charge is founded upon reason or was dictated by an intimidating power or by malice and personal ill will." Id., at 390. It blinks reality to say that the grand jury can adequately perform this important historic role if it is intentionally misled by the prosecutor-on whose knowledge of the law and facts of the underlying criminal investigation the jurors will, of necessity, rely. Unlike the Court, I am unwilling to hold that countless forms of prosecutorial misconduct must be tolerated-no matter how prejudicial they may be, or how seriously they may distort the legitimate function of the grand jury—simply because they are not proscribed by Rule 6 of the Federal Rules of Criminal Procedure or a statute that is applicable |